This invention relates to a color photographic material, more particularly to a color photographic material that has high chroma and that insures faithful reproduction of color hues even under illumination with a fluorescent lamp.
The recent advances in the photographic industry have been remarkable as regards the improvement in the quality of image of multi-layered silver halide color photographic materials. Three major elements of image quality are granularity, sharpness and fidelity of color reproduction and the levels of these factors have been markedly enhanced in modern photographic materials. It is generally held that prints and slides available today are usually more or less satisfactory to users.
As for the fidelity of color reproduction, substantial improvements have been achieved in color purity but the colors that have been considered to be unsuitable for reproduction by photography still remain in the same situation. In short, reproduction of color hues is still unsatisfactory in many respects. For example, purple and bluish purple that reflect light longer than 600 nm, or colors of green shades such as bluish green and yellow green are reproduced in an entirely different way than the original, often disappointing users.
Two major factors that relate to color reproduction are the spectral response and the interimage effect. As for the interimage effect, it is known in the art of multi-layered silver halide color photographic materials to add compounds that couple with the oxidation product of color developing agents to form development restrainers or precursors thereof. The development restrainers released from those "DIR compounds" inhibit development from occurring in other color-forming layers, thereby creating the interimage effect and hence achieving improved color reproduction. In color negative films, an effect similar to the interimage effect can be attained by using colored couplers in greater amounts than are necessary to cancel unwanted absorption. However, if colored couplers are used in excess amounts, the minimum density of the films will increase to cause considerable difficulty in determining the amount by which color density should be corrected in printing operation, and this often results in the deterioration of the quality of colors in the finished print. The techniques described above are mostly dedicated to improving color purity, rather than color hues, in color reproduction.
"Diffusible DIR" compounds which permit a greater mobility of restraining groups or precursors thereof are commonly used today and they have made great contribution to improvements in color purity. However, the interimage effect involves great difficulty in controlling its directionality and the use of such DIR compounds can alter color hues although they are effective in increasing color purity. For techniques of controlling the directionality of the interimage effect, see U.S. Pat. No. 4,725,529 and other references.
As for the spectral response which is the other major factor of color reproduction, U.S. Pat. No. 3,672,898 describes spectral responses that are appropriate for reducing the variations in color reproduction that occur on account of the use of different light sources in taking pictures. However, this technique is not effective for the purpose of correction the above-mentioned colors which are inherently low in the fidelity of color reproduction. A technique has also been proposed for combining spectral responses with the interimage effect. According to JP-A-61-34541 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and other references, this approach was used, with some success, to correct colors that are inherently low in the fidelity of color reproduction on color negative films. A typical example of this method consists of combining the inherent effects of conventional blue-, green- and red-sensitive layers with the interimage effect other than at the dominant wavelengths of the respective layers.
This technique, if performed successfully, is effective in improving to some extent the reproduction of certain colors but, in practice, in order for the interimage effect to be exhibited, not only the basic blue-, green- and red-sensitive layers but also a separate layer for exhibiting the interimage effect as well as other kinds of light-sensitive silver halides are necessary and this has increased the production cost due to the increase in the amount of silver and in the number of production steps. Further, the interimage effect achieved has been for from being satisfactory.
U.S. Pat. No. 3,672,898, supra teaches spectral responses that are appropriate for reducing the variations in color reproduction caused by the use of different light sources in taking pictures. The heart of this technique is to bring the spectral responses of blue- and red-sensitive layers close enough to that of a green-sensitive layer to reduce the variations in the sensitivity of each layer in response to the change in light source, especially in its color temperature, thereby minimizing the possible changes in color. A problem with this approach is that the spectral responses of the three light-sensitive are brought so close to one another that the resulting overlaps in the spectral sensitivity curves will lower the purity of colors. As is well known, this problem can be partly solved by emphasizing the interimage effect through the use of "diffusible DIR" compounds. However, even this improvement turned out to be very unsatisfactory in the fidelity of color reproduction when the light source was a fluorescent lamp as in the most common current practice of taking pictures indoors.